The present invention relates to a stacker for stimulable phosphor sheets, and more particularly to a stacker for temporarily storing a stack of stimulable phosphor sheets, the stacker having stock plates for placing the stimulable phosphor sheets thereon, the stock plates being displaceable in a prescribed direction to feed a desired stimulable phosphor sheet to a feed means and to position the stimulable phosphor sheet with reference to one side thereof.
There has recently been known a radiation image information recording and reproducing system for producing the radiation-transmitted image of an object using a stimulable phosphor material capable of emitting light upon exposure to stimulating rays. When a certain phosphor is exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation i subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation. The phosphor exhibiting such a property is referred to as a "stimulable phosphor".
In the radiation image recording and reproducing system employing such a stimulable phosphor, the radiation image information of an object such as a human body is stored in a sheet having layer of stimulable phosphor and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image information signal that is electrically processed for generating image information which is recorded as a visible image on a recording medium such as a photosensitive material or displayed as a visible image on a CRT or the like.
The radiation image recorded on the stimulable phosphor sheet is read in the radiation image recording and reproducing system as follows:
The radiation image recording and reproducing system includes an image reader for two-dimensionally scanning the stimulable phosphor sheet with a light beam such as a laser beam to cause the stimulable phosphor sheet to emit light, and detecting the light in time series with a light detector such as a photomultiplier to obtain image information. The stimulable phosphor sheet is usually two-dimensionally scanned by deflecting the light beam and applying the deflected light beam to the stimulable phosphor sheet in a main scanning direction, and simultaneously feeding the stimulable phosphor sheet mechanically on a conveyor belt or the like in an auxiliary scanning direction substantially normal to the main scanning direction.
After a stimulable phosphor sheet has been removed from a cassette and image information has been read from the stimulable phosphor sheet, the stimulable phosphor sheet is delivered to an eraser unit in which any residual image information is erased from the stimulable phosphor sheet. Thereafter, the stimulable phosphor sheet is stored back into the cassette for reuse. The cassette remains loaded in the image reader after the stimulable phosphor sheet has been removed and until it is placed again into the cassette. Therefore, while residual image information is being erased from the stimulable phosphor sheet, a process of reading an image from a next stimulable phosphor sheet cannot be effected, and hence the image reader cannot be put to efficient use.
One solution to the above problems is to provide a stacker in the image reader for holding a stack of stimulable phosphor sheets. The stacker holds stimulable phosphor sheets after image information has been read and erased therefrom. In operation, a cassette is loaded in the image reader and then a stimulable phosphor sheet stored in the cassette is removed, after which a stimulable phosphor sheet from which residual image information has been erased is removed from the stacker and stored into the cassette, which can then be unloaded from the image reader. Therefore, another cassette storing a next stimulable phosphor sheet can be loaded into the image reader, and image information borne by the stimulable phosphor sheet can be read by the image reader. As a consequence, the image reader can be used efficiently.
The stacker is arranged such that a stimulable phosphor sheet can be stored therein from one end of the stacker and can be removed therefrom from the opposite end of the stacker. The image reader must have stimulable phosphor sheet feed means at both ends of the stacker. With such stimulable phosphor sheet feed means incorporated, the image reader is considerably large in size.
When removing a stimulable phosphor sheet from the stacker, the stimulable phosphor sheet may be positionally displaced in its transverse direction. The displaced stimulable phosphor sheet cannot smoothly be fed by the feed means. The stimulable phosphor sheet removed from the stacker with such a positional error is placed out of a proper reading position in the process of reading image information from the stimulable phosphor sheet. As a result, image information cannot accurately be read from the stimulable phosphor sheet.